\[1)\ 7,\ \ \ 8,\ \ \ 12,\ \ \ 11.\]
\[Пусть\ одна\ часть\ равна\ x:\]
\[AB = 7x;\ \ \ BC = 8x;\]
\[CD = 12x;\ \ \ AD = 11x;\]
\[AB + CD = 19x;\]
\[BC + AD = 19x;\]
\[AB + CD = BC + AD.\]
\[Ответ:\ \ да.\]
\[2)\ 7,\ \ \ 12,\ \ \ 8,\ \ \ 11.\]
\[Пусть\ одна\ часть\ равна\ x:\]
\[AB = 7x;\ \ \ BC = 12x,\]
\[CD = 8x;\ \ \ AD = 11x;\]
\[AB + CD = 15x;\]
\[BC + AD = 23x;\]
\[AB + CD \neq BC + AD.\]
\[Ответ:\ \ нет.\]